Generally, a portion of a joint between an outer steel plate of a refrigerator and an inner resin molded part thereof is assembled by a table board, a lid, and chassis, all of which are formed by injection molding of resins. Typically, liquid urethane is injected between inner and outer walls of the refrigerator, followed by foaming and solidification at a proper temperature, to form a heat insulation layer of the refrigerator. In the liquid urethane, which is a raw material of such a foamed polyurethane heat insulation layer, a foaming agent such as Freon is used to produce a foam. Such a foaming agent usually remains in the foam even after foaming, thereby improving heat insulation performance.
However, the foaming agent contacts and chemically erodes a resin portion at which stress is concentrated during manufacture or use of a refrigerator, thereby causing cracking of a resin molded article. Thus, a resin for refrigerators is required to be resistant to the foaming agent.
Generally, rubber-modified aromatic vinyl copolymer resins such as an acrylonitrile-butadiene-styrene copolymer (ABS) resin have been mainly used as a resin for refrigerators. This is because the ABS resin has excellent properties in terms of stiffness, impact resistance and moldability, has high gloss to provide good appearance, and exhibits excellent chemical resistance to Freon (CFC-11), which is used as a foaming agent for hard urethane foams.
However, as existing foaming agents have been found to destroy the ozone layer, eco-friendly foaming agents such as hydrofluoroolefin (HFO) foaming agents, which have very low global warming potential (GWP) and ozone depletion potential (ODP) values and high foaming efficiency, are being developed. Such eco-friendly foaming agents cause stronger chemical erosion than existing foaming agents, and thus a resin for refrigerators used with the eco-friendly foaming agents is also required to have a higher level of chemical resistance.
For example, high impact polystyrene (HIPS) is chemically resistant enough to prevent cracking due to chemical erosion caused by HFO foaming agents. However, since HIPS has limitations in stiffness, impact resistance, and appearance, it is difficult to apply HIPS to medium and large size refrigerators.
Therefore, there is a need for a thermoplastic resin composition which has excellent properties in terms of chemical resistance, stiffness, and impact resistance to prevent chemical erosion caused by eco-friendly foaming agents and can be applied to various applications such as a material for a refrigerator inner case.